I'm a sophomore in highschool and I am planning an experiment with ferrofluids for a science fair next year. In my experiment, I would like to test whether the heat of a ferrofluid affects the size and number of spikes of ferrofluid that is magnetized. I want to put ferrofluids of different temperatures in different tubes. I would then place a magnet beneath the tubes and measure the number of spikes and record their heights. I have some questions though:

1.) What should the tubes be made out of? I would like a medium that is clear and does not block the magnetic field much.

2.) What kind of magnet should I use? I am thinking neodymium perhaps.

3.) Will heating or cooling the ferrofluids hinder their ability to become magnetized in multiple trials?

4.) What exactly does the height or number of spikes display? For example, the strength of the magnetic field.

I was also considering doing a different ferrofluid-related experiment:
Testing the temperature of the medium on the effect of surface temperature. From research I can tell that more spikes means less surface tension.

Or, there is always the possibility of testing the temperature of the magnet.

Thanks in advance! If you can't answer all the questions that is alright. Also tell me if you like the experiment of testing for the surface tension more.

I'm a sophomore in highschool and I am planning an experiment with ferrofluids for a science fair next year. In my experiment, I would like to test whether the heat of a ferrofluid affects the size and number of spikes of ferrofluid that is magnetized. I want to put ferrofluids of different temperatures in different tubes. I would then place a magnet beneath the tubes and measure the number of spikes and record their heights. I have some questions though:

Great to see interest in ferrofluids: I used it in my master thesis

Originally Posted by guitarace372

1.) What should the tubes be made out of? I would like a medium that is clear and does not block the magnetic field much.

I don't think it matters much. Glass should be fine. Be careful with plastic: the small particles tend to stick to it, making it less transparent.

Originally Posted by guitarace372

2.) What kind of magnet should I use? I am thinking neodymium perhaps.

The more powerful the magnet, the more powerful the effect, so NeFeB is great.

Originally Posted by guitarace372

3.) Will heating or cooling the ferrofluids hinder their ability to become magnetized in multiple trials?

No, the particles are very small and typically have only one Weiss-area. Even if you go above Curie-Temperature, I doubt there would be a permanent effect. Something that could happen is that the oil deteriorates (burns), or the surfractants which keep the particles from clogging together to become damaged. In that case the ferrofluid is ruined.

Originally Posted by guitarace372

4.) What exactly does the height or number of spikes display? For example, the strength of the magnetic field.

You can describe the behaviour of a ferrofluid with an extended Bernoulli-equation, adding a magnetic term with B_1 and B_2 the magnetic flux density and M_s the magnetisation of the ferrofluid. This last parameter is pretty constant (but maybe not over temperature), since ferrofluid very quickly saturates. For a similar ferrofluid as you use, we estimated a saturation magnetisation of 40 kA/m. The pressure difference should correlate somehow with the height of the spikes:
The second important effect is indeed the surface tension, which will try to keep the ferrofluid as close together as possible: higher surface tension means less 'pointy' spikes, less pointy spikes means that they will be lower with the same amount of ferrofluid.

What happens exactly is that the total energy in the system minimises: the sum of potential gravitational energy, magnetic energy and surface energy "wants" to be as small as possible.

Originally Posted by guitarace372

I was also considering doing a different ferrofluid-related experiment:
Testing the temperature of the medium on the effect of surface temperature. From research I can tell that more spikes means less surface tension.

This makes sense. Such an experiment would allow you to compare the results of the first experiment with this one: does the temperature mainly changes the surface tension, or is there another (magnetic) effect of the temperature...

An extra note: the ferrofluid you use is probably not a real ferrofluid, but something in between a magnetorheological fluid (particle size 1 Ám and up) and a ferrofluid (particle size 10 nm and down). This is good for you, because it has a higher saturation magnetisation, and thus a larger effect, but the particles are less dispersed and start forming chains that are harder to break: the viscosity changes.